1. Field of the Invention (Technical Field)
The present invention relates to sparging systems and methods of in-situ groundwater remediation for removal of contamination including dissolved chlorinated hydrocarbons and dissolved hydrocarbon petroleum products. Remediation of saturated soils may also be obtained by employment of the present invention. In particular, the present invention is directed to the use in injection wells of microfine bubble generators, matched to substrates of selected aquifer regions, for injection and distribution of said bubbles containing oxidizing gas through said aquifer. Further, the present invention relates to selectively encapsulating gases including oxygen and ozone in duo-gas bubbles which, in the presence of co-reactant substrate material acting as a catalyst, are effective to encourage biodegradation of leachate plumes which contain biodegradable organics, or Criegee decomposition of leachate plumes containing dissolved chlorinated hydrocarbons.
2. Background Prior Art
The introduction of air bubbles into aquifers for the purpose of remediation is a recent advancement in in-situ treatment of groundwater (Marley, et al., 1992; Brown et al., 1991). Contained air entrainment has been used for many years to provide vertical movement of water in low-head aquariums and in the development of public well supplies (Johnson, 1975). Aeration of aquifers for plume management was suggested to accelerate bacterial degradation of dissolved organic compounds (JRB, 1985). As bubble volume increases in density above re-aeration needs by approaching ratios beyond 1 to 10 (1 water to 10 air), gas transfer begins to dominate. In this case, volatile organics may be physically transported from the saturated aquifer to the overlying unsaturated zone (vadose zone).
There is a well-recognized need for a simple test to evaluate a potential site to assist with design of sparging systems deployed on a remediation site. Whereas hydraulic tests have been performed for some period of time based upon the well-known Theis equation, the introduction of air bubbles (particularly microscopic bubbles) is new. Also, whereas the introduction of air to the pressure vessel is continuous, the production of bubbles, particularly the microscopic variety, is a discrete discontinuous process. Bubbles, once generated, may take preferential pathways, determined largely by the substratum and, secondarily, by the introduction of pressure (Ji, et al., 1993).
Applicant is aware of prior art devices that have used injection of air to facilitate biodegradation of plumes.
U.S. Pat. No. 5,221,159 to Billings shows injection of air into aquifer regions to encourage biodegradation of leachate plumes which contain biodegradable organics together with simultaneous soil vacuum extraction.
Also in U.S. Pat. No. 4,730,672 to Payne, there is disclosed a closed-loop process for removing volatile contaminants. However, Payne deals only with volatile contaminants. Payne discloses a withdrawal well surrounded by multiple injection wells. Pressurized air is injected into the groundwater through the injection wells, and is withdrawn under vacuum from the withdrawal well whereupon contaminants are removed from the air stream and the air is then recycled through the system. The U.S. Pat. No. 4,588,506, to Raymond et al. discloses the injection of a diluted solution of hydrogen peroxide into a contaminated soil for enhancing biodegradation of organic contaminants in the soil. Raymond discloses intermittent spiking of the hydrogen peroxide concentration to eliminate biota to increase soil permeability. Raymond has the disadvantage of failing to deliver oxygen through the system, and depends on a complicated process of hydrologic management of the subsurface which has rendered the process uneconomical.
In U.S. Pat. No. 5,167,806 to Wang et al. there is disclosed apparatus for treatment of a contaminated liquid stream comprising generating extremely fine gas bubbles through porous diffusers, wherein the gas may be a combination of air and ozone. One process disclosed by Wang involves removing dissolved organics from contaminated groundwater by means of generating micro gas bubbles. In the first stage of the process for removing dissolved organics, which involves generating bubbles, no vacuum is employed, as gas bubbles are completely dissolved by the method. Wang teaches an enhanced dissolved aqueous reaction.
In U.S. Pat. No. 4,832,122 to Corey et al. is disclosed an in-situ method for removing contamination from groundwater comprising a horizontal well positioned in the saturated zone which has multiple apertures for injecting gas. The apertures are shown in the figures to be sequentially arranged and closely spaced so that the bubbles zones produced from each one would overlap with the adjacent zones. Corey et al. teaches that the configuration of the injection system is dictated by the size and shape of the plume, drilling economics, and the subsurface geology (column 1, lines 4-9, 41-43, 64-68; column 2, lines 1-8, 43-48). Corey also teaches an enhanced dissolved aqueous reaction.
U.S. Pat. No. 4,614,596 to Wyness discloses a method for dissolving a gas in an aqueous stream which comprises diffusing a gas in an aqueous stream to produce small gas bubbles which are rotated to provide a long flow distance over which the bubbles have increased contact time. The figures show that the bubbles are dispersed within and outward from a vessel, or well casing, by maximizing the dispersal of bubbles from a well casing and maximizing contact with the bubbles. Wyness also teaches an enhanced dissolved aqueous reaction.
Notwithstanding the teachings of Wang et al., Corey et al., and Wyness, there has not been shown a sparging system for remediating a site in a controlled manner of poorly biodegradable organics, employing oxidizing gas encapsulated in microbubbles generated from microporous diffusors matched to soil porosity pulsed in a wave form for even distribution through the substrate (aquifer structure) employing a co-reactant in the form of substrate material. Further, the prior art fails to show matching of micron sized bubble formation with substrate material of a selected aquifer or to show the beneficial effect of uniform distribution of sized bubbles through such a formation by means of a pulsed wave form without fracturing said substrate. The present invention accomplishes this by injecting micron size bubbles into aquifer regions in combination with substrate materials acting as a catalyst to encourage biodegradation of leachate plumes which contain biodegradable organics by means of a gas/gas/water reaction which overcomes at least some of the disadvantages of prior art.
The present invention relates to injection of oxidizing gas in the form of microfine bubbles into aquifer regions by means of a sparging system which includes one or more injection wells to encourage in-situ remediation of subsurface leachate plumes by means of a gas-gas-water reaction. The present invention is directed to sparging systems and methods of in-situ groundwater remediation in combination with co-reactant substrate materials acting as a catalyst to encourage biodegradation of leachate plumes for removal of dissolved chlorinated hydrocarbons and dissolved hydrocarbon petroleum products. Remediation of saturated soils may also be obtained by employment of the present invention. In particular the present invention employs sparging apparatus including microporous bubble generators for generating micron sized duo-gas bubbles into aquifer regions by means of one or more vertically arranged injection wells having a bubble chamber for regulating the size of bubbles. The sparging system of the present invention encourages biodegradation of leachate plumes which contain biodegradable organics or Criegee decomposition of leachate plumes containing dissolved chlorinated hydrocarbons.
The following systems and methods for removing contaminants from soil and an associated subsurface groundwater aquifer using Microporous diffusers and duo-gas systems are particularly useful in that they promote extremely efficient removal of poorly biodegradable organics, particularly dissolved chlorinated solvents, without vacuum extraction, and wherein remediation occurs by destroying organic and hydrocarbon material in place without release of contaminating vapors.
In the present invention the groundwater and soil remediation system comprises oxidizing gas encapsulated in microbubbles generated from microporous diffusers matched to soil porosity. A unique bubble size range is matched to underground formation porosity and achieves dual properties of fluid like transmission and rapid extraction of selected volatile gases, said size being so selected so as to not to be so small as to lose vertical mobility. In order to accomplish a proper matching, a prior site evaluation test procedure is devised to test effectiveness of fluid transmission at the site to be remediated.
The advantage of controlled selection of small bubble size is the promotion of rapid extraction of selected volatile organic compounds, such as PCE, TCE, or DCE by incorporating the exceptionally high surface to gas volume ratio. The dual capacity of the small production and;rise time is matched to the short lifetime of an oxidative gas, such as ozone to allow rapid dispersion into water saturated geological formations, and extraction and rapid decomposition of the volatile organic material. The unique apparatus of the present invention provides for extraction efficiency with resulting economy of operation by maximizing contact with oxidant by selective rapid extraction providing for optimum fluidity to permit bubbles to move like a fluid through media which can be monitored.
The use of microporous bubble generators provides a more even distribution of air into a saturated formation than the use of pressurized wells. A microfine sparge system installed to remediate contaminated groundwater is made more cost-effective by sparging different parts of the plume area at sequenced times. Through the proper placement of bubble generator locations and sequence control, any possible off-site migration of floating product is eliminated. With closely spaced bubble generators, water mounding is used to advantage in preventing any off-site escape of contaminant. The mounding is used to herd floating product toward extraction sites.
In the present invention, the concept of microfine sparge system manipulation is predicated upon a thorough knowledge of the features of the groundwater or saturated zones on a site selected for remediation. Balancing the volume of air to the microfine system sparge loci enables control of sparging efficiency and balancing of any downgradient movement of a contaminated plume while remediation is accomplished. Critical to microfine sparge system design and accomplishment of any of the above points is to initially perform a xe2x80x9csparge point testxe2x80x9d for the purpose of evaluating the characteristics of the site for matching purposes.
Furthermore, the present invention overcomes the limitations expressed above of the prior technology. The invention employs the well recognized Criegee mechanisms which describes the gaseous reaction of ozone with the incoming PCE, TCE and DCE, and vinyl chloride into microbubbles produced by bubble generators with the resultant products then hydrolysed, i.e., reacted with water to decomposed into HCl and CO2. It is this physical/chemical reaction which produces the rapid removal rate employed by the present invention (see reference Maston S 1986, xe2x80x9cMechanisms and Kinetics of Ozone Hydroxal Radical Reactions with Model Alafadic and Olanfadic Compounds:, Ph.D. Thesis, Harvard University, Cambridge, Mass.).
Unlike the prior art, the contaminated groundwater is injected with an air/ozone mixture wherein microfine air bubbles strip the solvents from the groundwater and the encapsulated ozone acts as an oxidizing agent to break down the contaminants into carbon dioxide, very dilute HCl and water. This process is also known as the C-Sparger(trademark) process.
Accordingly, the object and purpose of the present invention is to provide microporous diffusors for removal of contaminants from soil and associated subsurface groundwater aquifer, without requiring vacuum extraction.
Another object is to provide duo-gas systems to be used in combination with the microporous diffusors to promote an efficient removal of poorly biodegradable organics, particularly dissolved chlorinated solvents, without vacuum extraction.
A further object is to provide for economical and efficient remediation of contaminated groundwater by providing a calculated plan of sparging different parts of a plume area at sequenced times.
Yet a further object is to control off-site migration of floating product by employing a water mounding technique which effectively herds floating product to extraction sites.
Another object is to provide microfine sparge system manipulation predicated on performance of a site evaluation test.
A further object is to provide that remediation occurs by destroying organic and hydrocarbon material in place without release of contaminating vapors to the atmosphere.
Yet a further object is to obtain economy of operation by maximizing contact with the oxidant to achieve selective rapid extraction.
Another object is to provide a microfine sparge system providing for optimum fluidity to permit bubbles to move like a fluid through media.
The invention will be described for the purposes of illustration only in connection with certain embodiments; however, it is recognized that those persons skilled in the art may make various changes, modifications, improvements and additions on the illustrated embodiments all without departing from the spirit and scope of the invention.